G4 Cube FWUpdate -->boot fiasco

[Karl-Heinz Haag <kh@lux.in-berlin.de>]

Hello, 
I'm new to this group and to the ppc/apple hardware. 
With Debian I have experiences for several years ... on the i386 platform. 

In Mid-May I bought a G4 Cube. 
In general: it is the the 'new' (for me) hardware I have difficulties with. 

After some fiddling with MacOS and MacOSX on my Cube I decided to put
'my' beloved Debian additionally on the HDD. 

This decision resulted in a three-system boot configuration, booting
Debian as default :-)
With the G4 Cube having a so-called NewWorld PowerMac, I achieved the
multi-booting by a Apple_Bootstrap partition activated by 
ybin and /etc/yaboot.conf.
A nice thing I found by access was booting with the 'Option' key which
also in a kind of GUI showed a Linux(penguin) boot icon choosable by
mouse (plus a bootable CD if inserted).

All this is lost now! 
For I did the newest "recommended" 'G4 Cube FWUpdate' version 4.1.8 
I did it having tested the additional RAM before. 
I had not thought of it damaging completely the boot configuration, even
the boot GUI apple-feature.

The new situation:
1) Booting into OpenFirmware now still shows the linux entry but it 
   doesn't boot Debian any more. 
2) Booting with the 'Option' key pressed now flickers up the boot 'GUI'
   for a short moment. In it only the boot volume choosed in one of the
   MacOSes can be seen. Then I get an OpenFirmware prompt. There I only
   see the possibility typing 'boot mac-os' to get a system.
3) Additionaly now I haven't any possibility to boot from a CD. 
   Neither pressing 'c' nor with the Option key.

What can I do get a boot status similar to that before the RomUpdate? 
Thanks a lot for hints.

Karl-Heinz